NamedTuple doesn’t support overriding __new__ #526
Description
I expected the following to work like with collections.namedtuple, but it doesn’t:
_FooBase = NamedTuple('_FooBase', [('a', FrozenSet[str])])
class Foo(_FooBase):
def __init__(self, a: Iterable[str]):
super().__init__(frozenset(a))but I get:
In [3]: Foo(['x'])
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-9-a93a09ef10e2> in <module>()
----> 1 Foo(['x'])
<ipython-input-8-cbd998f4721b> in __init__(self, a)
3 class Foo(_FooBase):
4 def __init__(self, a: Iterable[str]):
----> 5 super().__init__(frozenset(a))
6
TypeError: object.__init__() takes no parametersWith the 3.6 syntax, there’s an earlier error:
In [2]: class foo(NamedTuple):
...: a: FrozenSet[str]
...: def __init__(self, a: Iterable[str]):
...: super().__init__(frozenset(a))
...:
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-3-c99525ef7a4f> in <module>()
----> 1 class foo(NamedTuple):
2 a: FrozenSet[str]
3 def __init__(self, a: Iterable[str]):
4 super().__init__(frozenset(a))
5
/usr/lib/python3.6/typing.py in __new__(cls, typename, bases, ns)
2152 for key in ns:
2153 if key in _prohibited:
-> 2154 raise AttributeError("Cannot overwrite NamedTuple attribute " + key)
2155 elif key not in _special and key not in nm_tpl._fields:
2156 setattr(nm_tpl, key, ns[key])
AttributeError: Cannot overwrite NamedTuple attribute __init__